Redispersing agents for redispersible polymer powders and redispersible polymer powders including same

ABSTRACT

The invention relates to a redispersible polymer powder including a polymer to be redispersed and an ortho-cresol based condensation polymer or salt thereof and methods for manufacturing same. More particularly, the invention relates to the use of an ortho-cresol based condensation polymer as a redispersing aid in a redispersible polymer powder.

The present invention relates to redispersing aids for use in themanufacture of redispersible polymer powders and processes for makingsame. In particular, the invention relates to the use of ortho-cresolbased condensation polymers, for example, ortho-cresol sulfonic acidformaldehyde condensates, and their salts as redispersing aids inredispersible polymer powder systems. The invention further relates toredispersible polymer powders that include such a redispersing aid andcompositions or systems including such redispersible polymer powders.

The use of redispersible film forming polymers in powder form findswidespread use throughout a number of industries. For example, suchredispersible film forming polymers are used as construction binders fortile adhesives, synthetic resin plasters, floor leveling mixes and inareas where a waterless system is generally desirable. These systems ingeneral are produced by the dry blending of the raw materials, such assand, cement, calcium carbonate, silica flour, modified cellulose basedthickeners, and the dry polymer powder, to obtain a ready to usefinished product for site mixing where water is added at the point ofuse. These systems are advantageous as they avoid the need for a twocomponent system, one component containing an aqueous polymer dispersionand the other component containing the powder component which maycontain a hydraulic setting component such as cement. Avoiding suchsystems may be advantageous for a number of reasons such as economy,utility and environmental considerations.

To obtain a film forming polymer in powder form, a liquid dispersion ofthe polymer is subjected to a drying operation where the water isremoved by a suitable method such as spray drying or freeze drying.Spray drying is a widely used and understood method that gives a finepowder which, under well controlled predetermined conditions, does nothave to be further processed. This method is therefore generallypreferred.

In order to manufacture a redispersible film forming polymer powder withglass transitions below 50° C., it is generally necessary to add to theliquid dispersion before spray drying a quantity of redispersing aid.Redispersing aids act to coat the individual polymer particles toprevent irreversible primary particle formation. Such aids alsoadvantageously increase the yield during the spray drying process byminimizing sticking of the dried polymer to the walls of the spraydryer. The redispersing aid may also improve the storage stability ofthe polymer powder by minimizing “blocking” (the thermoplastic fusion ofthe polymer particles under weight pressure), and should generally havesome hydrophilic properties to aid redispersability of the polymerpowder on the reintroduction of water.

The redispersible polymer powders known to date generally comprise aredispersing aid that is water soluble and which is generally added tothe polymer dispersion before spray drying. As stated above, thisadvantageously prevents or reduces the formation of primary particlesduring the spray drying operation.

Polyvinyl alcohols have historically been used as redispersing aids forethylene vinyl acetate (EVA) dispersions for many years. For example,U.S. Pat. No. 3,883,489 assigned to Hoechst Aktinengellschaft makes useof polyvinyl alcohol as a redispersing aid for ethylene vinyl acetatedispersions. Whilst not as effective, polyvinyl alcohols can also beused as redispersing aids in the manufacture of redispersible acrylic orstyrene-acrylic polymer powders. For example, U.S. Pat. No. 5,567,750assigned to Wacker-Chemie GmbH makes use of a polyvinyl alcohol alongwith an amino functional polyvinyl alcohol for the manufacture of aredispersible styrene-acrylic polymer powder. U.S. Pat. No. 5,519,084assigned to Air Products and Chemicals makes use of a polyvinyl alcoholas a redispersing aid with an acrylic polymer consisting of up to 15%olefinically unsaturated carboxylic acid. However, polyvinyl alcoholsare not entirely satisfactory as redispersing aids for acrylics orstyrene acrylics or styrene butadiene dispersions as they are forethylene vinyl acetate dispersions.

The use of salts of arylsulfonic acid-formaldehyde condensates asredispersing aids is also known, especially for acrylic dispersions.German Offenlegungsschrift 24 45 813 translated as “Redispersiblesynthetic powder and method of production” describes the use of phenolsulfonic acid formaldehyde condensates and naphthalene sulfonic acidformaldehyde condensates and their alkali salts or their alkali earthmetal salts as redispersing aids for redispersible powders. U.S. Pat.No. 5,225,478 assigned to BASF also describes the use of phenol sulfonicacid formaldehyde condensates and their alkali salts or alkali earthmetal salts as a redispersing aid. U.S. Pat. No. 6,028,167 assigned toBASF describes an improvement by controlling the molecular weight of theredispersing aids. Likewise, Australian Patent No. 718,907 describes animprovement in naphthalene sulfonic acid formaldehyde condensates bycontrolling or restricting the molecular weight of the redispersingaids.

The issue of molecular weight control is generally considered importantin the manufacture of redispersing aids for redispersible powders. Forexample, U.S. Pat. No. 6,028,167 describes in example S1 the method ofmanufacture for a phenol sulfonic acid formaldehyde condensate with amolecular weight of 750. Example S1 was repeated (as Example S2) withthe only change being the increased condensation time and hencemolecular weight. Example S2 was not as effective as Example S1 as aredispersing aid. During the manufacturing on an industrial scale,therefore, molecular weight control is an important parameter.Furthermore, there is always a residual amount of high molecular weight(>10,000) components remaining after reaction (Table 1 in samepatent-inventive example) This portion of the redispersing aid will notbe as effective as the lower molecular weight species that are requiredfor redispersing the polymer powder.

The present invention aims to provide an alternative redispersing aidfor use in the manufacture of redispersible polymer powders.Particularly, a redispersing aid that is suitable for use in systemsinvolving a polymer having a relatively low glass transitiontemperature. More particularly, the invention relates to the manufactureof an ortho-cresol sulfonic acid formaldehyde condensate based dimer oroligomer and its salts, and the use of such products as a redispersingaid. The invention advantageously further provides an industrial processthat will make the manufacture of such redispersing aids morereproducible in terms of molecular weight.

According to one aspect of the present invention there is provided aredispersible polymer powder including:

a polymer to be redispersed; and

an ortho-cresol based condensation polymer or salt thereof.

According to another aspect of the invention there is provided a methodfor manufacturing a redispersible polymer powder including:

forming a dispersion of a polymer to be redispersed and an ortho-cresolbased condensation polymer; and

drying the dispersion to form the redispersible polymer powder.

There is also provided a polymer powder manufactured by the method ofthe immediately preceding paragraph.

According to a further aspect the invention provides the use of anortho-cresol based condensation polymer as a redispersing aid in aredispersible polymer powder.

There is also provided a product including, as a binder, theredispersible polymer powder discussed in accordance with thisinvention. There is still further provided the use of such aredispersible polymer powder as a binder for a product, such as forexample hydraulically setting compositions, adhesives, coatingcompositions, synthetic resin renders, and for modifying buildingmaterials.

As used herein, the term “ortho-cresol based condensation polymer”primarily includes ortho-cresol sulfonic acid formaldehyde condensationpolymers and (ortho-cresol/phenol) sulfonic acid formaldehydecondensation polymers, but may also include within its ambit mixedcondensation polymers of ortho-cresol sulfonic acid with other monomerssuitable for such condensation reaction, more specifically theirsulfonated product.

Ortho-cresol is an important starting material for the redispersing aidof the invention and pivotal for the various applications of theredispersing aid of the invention. While not wanting to be bound by anytheory as to why the products of this invention are effective, thefollowing serves as a guide that is not intended to limit the scope ofthe invention in any way, but which serves as information as to the mostlikely synthesis products of the invention.

The ortho-cresol based condensation polymer or salt thereof is, in oneembodiment, an ortho-cresol sulfonic acid formaldehyde condensationpolymer which may be manufactured by a method comprising:

(i) sulfonating ortho-cresol with sufuric acid preferably under a slightexcess of sulfuric acid;

(ii) condensing the sulfonated ortho-cresol with formaldehyde.

The first step of this embodiment of the invention involves thesulfonation of ortho-cresol with sulfuric acid under slightly greaterthan equimolar concentration (i.e. slight excess of sulfuric acid).Sulfonation of ortho-cresol is generally an ortho/para reaction relativeto the hydroxyl group. However, sulfonation normally proceeds in thepara position relative to the hydroxyl group due to reasons such assteric hindrance, as opposed to the only ortho position that isavailable. This first step would predominantly form ortho-cresolsulfonic acid with the sulfonic group in the para position to thehydroxyl radical. The addition of the sulfuric acid preferably takesplace at from 35 to 60° C. with the final sulfonation preferably takingplace at higher temperatures (such as from 85 to 95° C.). The secondstep involves the condensation of the sulfonated ortho-cresol withformaldehyde. As condensation is predominantly ortho/para, thecondensation will only take place at the remaining ortho position. Thepredominant product manufactured is a dimer of two ortho-cresol sulfonicacid molecules.

According to an alternative embodiment the ortho-cresol basedcondensation polymer or salt thereof is an ortho-cresol sulfonic acidmixed condensation polymer which may be manufactured by a methodcomprising:

(i) sulfonating ortho-cresol with sufuric acid preferably under a slightexcess of sulfuric acid;

(ii) condensing the sulfonated ortho-cresol with a compatible monomer.

In this embodiment, the ortho-cresol sulfonic acid is used as amolecular weight regulator for the production of mixed condensationpolymers with monomers such as cresol (mixed isomers), phenol,resorcinol, naphthalene, meta-cresol, para-cresol as well as theirrespective sulfonated acids. Whilst other combinations of oligomers willbe present in the resultant reactant products, the products aregenerally low molecular weight species that are effective and are withinthe molecular weight range that is preferred for a redispersing aid forredispersible polymer powders. More importantly, high molecular weightspecies are significantly reduced or eliminated using the abovementioned steps. It is thought that this is true so long as thesulfonation of the ortho-cresol is complete in the first step (to reducethe reactive sites for condensation to only one remaining orthoposition), and a significant amount of ortho-cresol is used to regulatethe molecular weight of the final product. The final product may beneutralized prior to use with a base.

There are two preferred aspects to the manufacture of the ortho-cresolbased condensation polymer or salt thereof in accordance with theinvention. The first includes the use of ortho-cresol to form anortho-cresol sulfonic acid formaldehyde condensation polymer and itssalts as discussed above. The second preferred aspect is the use ofortho-cresol and phenol mixed, or ortho-cresol sulfonic acid and phenolsulfonic acid mixed as starting materials, to form anortho-cresol/phenol-sulfonic acid formaldehyde condensation polymer orits salts. The ortho-cresol may be mixed with phenol before sulfonationor the ortho-cresol sulfonic acid may be mixed with the phenol sulfonicacid prior to condensation. Other process modifications will be apparentto those skilled in the art, such modifications being included withinthe spirit of the present invention.

The ortho-cresol based condensation polymer or salt thereof, preferablyortho-cresol sulfonic acid formaldehyde condensate, is generally used inits form of its salts. The salts will generally include the alkali metalsalts or the alkaline earth metal salts. Ammonium salts or organicamines may also be used. Preferred salts are the calcium salts or thesodium salts or combination of these.

The present invention also provides for the use of ortho-cresol basedcondensation polymers or salts thereof, particularly ortho-cresolsulfonic acid formaldehyde condensate and its salts, as a redispersingaid in the preparation of redispersible polymer powders. Preferably theortho-cresol based condensation polymer or salt thereof is added at alevel of from about 1% to about 30% by weight of solid ortho-cresolbased condensation polymer or salt thereof relative to the solid polymerpowder, more preferably from about 1% to about 15%. This illustrates anadvantage of the inventive powders over the products of the prior artwhich generally require larger amounts of redispersing aid based on theweight of the polymer.

The polymers that may be used in combination with the ortho-cresol basedcondensation polymer or salt thereof are generally those with glasstransitions below 50° C. Most preferred are flexible polymers whichgenerally have a glass transition below 5° C. For example, polymersmanufactured using emulsion polymerisation techniques. Polymers may bepure acrylic polymers (example based on methylmethacrylate and alkylacrylates such as butyl acrylate), styrene-acrylic (example based onstyrene and alkyl acrylates such as 2-ethylhexyl-acrylate), vinylacetate copolymers with alkyl acrylate or ethylene or maleates, andstyrene-butadiene based polymers. More particularly, the polymer maypreferably contain two or more monomers selected from the groupconsisting of styrene, methylmethacrylate, vinyl acetate, butadiene,n-butyl acrylate, 2-ethylhexylacrylate, ethylacrylate, methylacrylate,ispropylacrylate, vinyl propionate, dibutyl maleate, ethylene,tert-butyl acrylate, methacrylic acid, acrylic acid, acrylamide,methacrylamide, hydroxyethyl methacrylate.

The type of polymer to be used within this invention, however, is notrestricted on the combination referred to above, but most polymers usedin industry, used in the manufacture of construction products, and usedas an anionic or nonionic dispersion polymer in water, will generally beable to be used with the ortho-cresol based condensation polymer or saltthereof so long as the two components are compatible when mixed inliquid form before drying, particularly spray drying. Examples of thesetypes of polymers are generally those referred to in the description inAustralian Patent No. 717,206 which is incorporated herein in itsentirety by reference thereto. The type of polymer is not critical forthe use of the invention.

The ortho-cresol based condensation polymer or salt thereof is generallymixed with the polymer dispersion before drying. The resultant mixtureis then preferably spray dried using conventional spray dryingtechniques. For example, rotating disc atomization, single fluid nozzlesor multi fluid nozzles are used for the atomization step along with adrying operation in a chamber preferably using air heated from 120 to180° C. The resultant polymer powder is preferably collected in cyclonesor filter bag houses. Anti-caking agents may also be metered in whilstthe polymer powder is suspended in the air stream.

Embodiments of the invention will now be discussed in more detail withreference to the following examples which are provided forexemplification only and which should not be considered limiting on thescope of the invention in any way.

EXAMPLES Preparative Example D1

A glass 1 liter laboratory reactor equipped with 2 dosing lines, avariable speed mechanical stirrer, a reflux condenser, a glassthermometer, and a water bath was loaded with 77 grams of deionisedwater, 0.8 grams of sodium bicarbonate, 0.5 grams of a nonyl phenolethoxylate with 30 moles of ethylene oxide, 0.35 grams of a solid sodiumsalt of a sulfated nonyl phenol ethoxylate with 30 moles of ethyleneoxide. To the above was added 17 grams from a feed mix 1 comprising 78grams of water, 2 grams of a nonyl phenol ethoxylate with 30 moles ofethylene oxide, 0.7 grams of a solid sodium salt of a sulfated nonylphenol ethoxylate with 30 moles of ethylene oxide, 5 grams ofacrylamide, 144 grams of butyl acrylate, and 96 grams of styrene and washeated to 85 degrees celcius. Once the temperature had reached 85degrees, 2 grams of a mix number 2 was added which comprised of 22 gramsof water with 1.6 grams of sodium persulfate. The reactor loading wasallowed to react for 10 minutes. The remaining of mixture 1 was then fedover 2 hours whilst the remaining mixture 2 was fed over 2 hours and 10minutes. The contents of the reactor flask was held at 85 degrees bycontrolling the temperature of the water bath. The agitator speed wasaround 400 rpm. At the end of the feeds, the reaction product was heldfor 30 minutes at 85 degrees. 0.5 grams of TBHP (70% solution) was thenadded in 2 grams of water and the reaction product was allowed to coolto room temperature. A mixture comprising 2 grams of ammonia in 2 gramsof water was then added to bring the pH above 7. The product wasfiltered through a 200 micron screen and gave a polymer dispersion witha solids content of 57% with an onset glass transition (as measured witha Shimadzu DSC-60 differential scanning colorimeter) of −3 degreesCelsius.

Example 1

A glass 3 liter laboratory reactor equipped with 1 dosing line, avariable speed mechanical stirrer, a reflux condenser and a water bathwas loaded with 350 grams of ortho-cresol and heated to 60 degreesCelsius. At 60 degrees, 390 grams of sulfuric acid (98%) was added over40 minutes and the temperature of contents was then heated at 85-95degrees Celsius for 75 minutes. The contents of the reactor were thereagain cooled to 60 degrees and 600 grams of water was added. A mixturecomprising 180 grams of formaldehyde (30% in water) and 800 grams ofwater was then dosed into the reactor over 30 minutes and the contentswere then heated at 85-95 degrees for 2.5 hours. The contents of thereactor was then cooled to room temperature and added to a solution ofCalcium hydroxide (280 grams) and water (1600 grams) and filtered. Theresultant mixture had a pH of 8.3 and a solids content of 22.5%. Theresultant mixture was foamy on neutralization with the base and clearlydemonstrated surfactant type properties.

Example 2

The procedure of example 1 was repeated but the 350 grams ofortho-cresol was replaced with 175 grams of ortho-cresol and 153 gramsof phenol and the calcium hydroxide was increased to 300 grams. Theresultant mixture had a pH of 8.7 and a solids content of 22.8%. Theresultant mixture was less foamy on neutralization with the base ascompared to example 1, but still clearly demonstrated surfactant typeproperties.

Example 3

Example 1 was repeated but the condensation time was increased from 75minutes to 7 hours. The product was slightly darker than example 1however, all other properties were similar (foamy on neutralization andpH of 8.4)

Comparative Example 1

Example 3 was repeated but the ortho-cresol was totally replaced withphenol. The product was similar in colour to example 1 but was not asfoamy on neutralization clearly demonstrating lower surfactant typeproperties and the likelihood of higher molecular weight species.

Example 4

The procedure in example 1 was repeated but the product was neutralizedwith 505 grams of Sodium hydroxide (46% in water) instead of the calciumhydroxide and water mix.

Comparative Example 2

Lomar D (a commercial high molecular weight sodium salt naphthalenesulfonate formaldehyde condensation product available from Cogins) wasmade into a 25% solution in water. The product was non foaming and verydark.

Example Powder P1

A mixture comprising 500 grams of water, 190 grams of example 1, 1000grams of example D1 and 5 grams of defoamer (Foamaster 8034e) and 3grams of Sodium Hydroxide (46% in water) was mixed and spray dried in a“Niro production minor” spray drier as manufactured by Niro Denmarkrefitted with a “Nubilosa” nozzle as manufactured by Nubilosa Germany.The inlet temperature was 130 degrees Celsius, and the air outlet wasset to 50% maximum. Fine talc was metered into the air stream at 2-3%based on solid polymer. The product was collected and theredispersabilty was evaluated when mixed with water and also when mixedwith sand, cement and water as a mixture. The product was veryredispersible.

Example Powder P2

Example powder P2 was prepared as per example powder P1 withredispersability aid example 2. The product obtained was very readilyredispersible with similar results as example powder P1.

Example Powder P3

Example powder P3 was prepared as per example powder P1 withredispersability aid example 3. The product obtained was slightly darkerthan example powder P1, however the redispersabilty was still the sameas example powder P1. This example shows that the reaction time of theredispersing aid is not influenced by the reaction time (condensationtime) as prior art examples (as they are in examples in U.S. Pat. No.6,028,167) and demonstrates a more consistent product that is not overlydependent on process conditions.

Comparative Example Powder CP1

Example powder CP1 was prepared as per example powder P1 withredispersability aid comparative example 1. The product obtained wasslightly less redispersible than example powder P1.

Example Powder P4

Example powder P4 was prepared as per example powder P1 withredispersability aid example 4. The product obtained was very readilyredispersible (more so than example powder P1) and was very hygroscopic.

Comparative Example Powder CP2

Example powder CP2 was prepared as per example powder P1 withredispersability aid comparative example 2. The product obtained was notredispersible due to the very high molecular weight of this condensationproduct.

The reference to any prior art in this specification is not, and shouldnot be taken as, an acknowledgment or any form of suggestion that thatprior art forms part of the common general knowledge in Australia.

The invention has been described by way of non-limiting example only andmany modifications and variations may be made thereto without departingfrom the spirit and scope of the invention described.

1. A redispersible polymer powder including: a polymer to beredispersed; and an ortho-cresol based condensation product or saltthereof.
 2. A redispersible polymer powder according to claim 1, whereinthe ortho-cresol based condensation product or salt thereof is anortho-cresol sulfonic acid formaldehyde condensation productmanufactured by a method comprising: (i) sulfonating ortho-cresol withsufuric acid; and (ii) condensing the sulfonated ortho-cresol withformaldehyde.
 3. A redispersible polymer powder according to claim 2,wherein the sulfonation step (i) is carried out under a slight excess ofsulfuric acid.
 4. A redispersible polymer powder according to claim 2,wherein the addition of the sulfuric acid to the ortho-cresol takesplace at from 35 to 60° C. and the final sulfonation takes place athigher temperatures from 85 to 95° C.
 5. A redispersible polymer powderaccording to claim 1, wherein the ortho-cresol based condensationproduct or salt thereof is an ortho-cresol sulfonic acid mixedcondensation product manufactured by a method comprising: (i)sulfonating ortho-cresol with sufuric acid; and (ii) condensing thesulfonated ortho-cresol with a compatible monomer.
 6. A redispersiblepolymer powder according to claim 5, wherein the sulformation step (i)is carried out under a slight excess of sulfuric acid.
 7. Aredispersible polymer powder according to claim 5, wherein thecompatible monomer is selected from cresol, phenol, resorcinol,naphthalene, meta-cresol, para-cresol and their respective sulfonatedacids.
 8. A redispersible polymer powder according to claim 7, whereinthe compatible monomer is phenol.
 9. A redispersible polymer powderaccording to claim 1, wherein the ortho-cresol based condensationproduct or salt thereof is an alkali metal salt or the alkaline earthmetal salt.
 10. A redispersible polymer powder according to claim 9,wherein the ortho-cresol based condensation product is a calcium salt orsodium salt or combination thereof.
 11. A redispersible polymer powderaccording to claim 1, wherein the ortho-cresol based condensationproduct or salt thereof is added at a level of from about 1% to about30% by weight of solid ortho-cresol based condensation product or saltthereof relative to the solid polymer powder.
 12. A redispersiblepolymer powder according to claim 11, wherein the ortho-cresol basedcondensation product or salt thereof is added at a level of from about1% to about 15%.
 13. A redispersible polymer powder according to claim1, wherein the polymer to be redispersed has a glass transition below50° C.
 14. A redispersible polymer powder according to claim 13, whereinthe polymer to be redispersed includes at least one flexible polymerhaving a glass transition below 5° C.
 15. A redispersible polymer powderaccording to claim 1, wherein the polymer to be redispersed is selectedfrom pure acrylic polymers, styrene-acrylic polymers, vinyl acetatecopolymers with alkyl acrylate or ethylene or maleates,styrene-butadiene based polymers and combinations thereof.
 16. Aredispersible polymer powder according to claim 15, wherein the polymerto be redispersed includes two or more monomers selected from the groupconsisting of styrene, methylmethacrylate, vinyl acetate, butadiene,n-butyl acrylate, 2-ethylhexylacrylate, ethylacrylate, methylacrylate,ispropylacrylate, vinyl propionate, dibutyl maleate, ethylene,tert-butyl acrylate, methacrylic acid, acrylic acid, acrylamide,methacrylamide, and hydroxyethyl methacrylate.
 17. A redispersiblepolymer powder according to claim 1, wherein the ortho-cresol basedcondensation product or salt thereof is mixed with a dispersion of thepolymer to be redispersed before drying thereof and the resultantmixture is then spray dried using conventional spray drying techniques.18. A method for manufacturing a redispersible polymer powder including:forming a dispersion of a polymer to be redispersed and an ortho-cresolbased condensation product; and drying the dispersion to form theredispersible polymer powder.
 19. A method for manufacturing aredispersible polymer powder according to claim 18, wherein thedispersion of polymer to be redispersed and an ortho-cresol basedcondensation product or salt thereof is spray dried to form saidredispersible polymer powder.
 20. A method for manufacturing aredispersible polymer powder according to claim 19, wherein thedispersion is atomized using rotating disc atomization, single fluidnozzles or multi fluid nozzles and dried in a chamber using air heatedfrom 120 to 180° C., and wherein the resultant redispersible polymerpowder is collected in cyclones or filter bag houses.
 21. A method formanufacturing a redispersible polymer powder according to claim 18,wherein an anti-caking agent is metered into the polymer powder whilethe polymer powder is suspended in the air stream.
 22. A redispersiblepolymer powder manufactured by the method of claim
 18. 23. (canceled)24. A product including, as a binder, the redispersible polymer powderaccording to claim
 1. 25. A product according to claim 24, said productbeing selected from hydraulically setting compositions, adhesives,coating compositions, synthetic resin renders, and modified buildingmaterials.
 26. A method of manufacture of a product comprising a binder,said method comprising the step of incorporating a redispersible polymerpowder according to claim 1 as a binder in the product.
 27. The methodaccording to claim 26, wherein the product is selected fromhydraulically setting compositions, adhesives, coating compositions,synthetic resin renders, and modified building materials.